The risks of early and late bleeding, placenta previa, abruptio placentae, and premature and prolonged rupture of membranes increase with increasing levels of maternal smoking during pregnancy. However, the degree of risk appears to vary depending on other maternal factors. The objectives of this study are: 1) to identify women in terms of age-parity, socioeconomic status, height, weight, weight gain, hemoglobin level, past obstetric and medical history, use of medical services, and other factors who will be at highest risk for these complications if they smoke; 2) to trace the progression of these complications prospectively to preterm or term delivery and to perinatal death or survival, weighing the relative importance of maternal smoking and of other risk factors in the process; 3) to serve as a model for future prospective studies by identifying mothers at maximum risk of complications and by determining an optimum comparison group. Data from the Ontario Perinatal Mortality Study are now being analyzed to fulfill these objectives. Preliminary findings indicate the relative importance of maternal smoking and other antecedent factors to a) the occurrence of selected pregnancy complications and b) the incidence of adverse pregnancy outcomes with and without these complications. The current application is for support for a similar analysis of data from the Jerusalem Perinatal Study, which have been made available to us since the original application. Advantages of using a second data set are that the consistency of results in a different population can be tested; Jerusalem data are more recent, and some complications of interest were more completely ascertained in Jerusalem. Data from both studies will be used a) to calculate sample sizes needed in prospective studies of pregnancy complications and b) to produce a nomogram to assess the risk of pregnancy complications and the risk of adverse pregnancy outcomes for women with different profiles, and to measure the impact of smoking on these risks.